A new species endemic to Chiapas, Mexico, Stenanona migueliana (Annonaceae), is described and illustrated. The new species has affinity with S. stenopetala, from which it differs in the length of the floral pedicel, size of the sepals, arrangement of the ovules, and surface texture of the fruit. A key to the Mexican species of Stenanona is presented.

Stenanona Standi., is a Neotropical genus of dwarf to small trees that comprises 14 described species, geographically distributed from southern Mexico to southern Colombia at elevations ranging from 0 to 1,250 m. Species of Stenanona inhabit tropical, moist, evergreen, and montane rain forests (Schatz and Maas, 2010).

The new subfamilial and tribal classification of Annonaceae places Stenanona within subfamily Malmeoideae, tribe Miliuseae (Chatrou et al., 2012). In the most recent molecular phylogenetic analysis of Annonaceae (Chatrou et al., 2012), based on eight plastid markers, two Stenanona species are shown as monophyletic and sister to a paraphyletic Desmopsis, a genus also centered in Mesoamerica. The divergence of Stenanona and Desmopsis based on Penalized Likelihood (PL) was estimated to be a mean age of 35 Ma (SD = 7Ma), whereas the mean age estimated with BEAST was 15 Ma (HPD 95% = 10-20Ma), indicating a diversification between Mid-Eocene and Mid-Miocene (Pirie and Doyle, 2012).

In Mexico (Chiapas, Oaxaca, Tabasco, and Veracruz), have been recorded seven of the 15 species of Stenanona, six of which are endemic to Mexico, with only one species, Stenanona stenopetala (Donn.Sm.) G.E.Schatz, extending its range to Guatemala and Belize (Schatz and Maas, 2010). The petal morphology of Stenanona, in combination with the pink to blood red color of the flower, is suggestive of a fly pollination syndrome (Schatz, 1987). This character could be related to the high rate of diversification of this genus (Couvreur et al., 2011; Erkens et al., 2012).

During the course of a series of botanical explorations in a protected area in the state of Chiapas, Mexico, which is in the process of being enacted as a reserve, we collected a species of Stenanona with a unique combination of leaf, flower, and fruit characteristics that permitted us to conclude that it is new to science. A description of the new species, with an accompanying illustration and photos, and a key to the Mexican species of Stenanona, are presented.

Distribution and ecology: -Known only from two localities, Stenanona migueliana grows on a karstic zone at approximately 900-1,150 m above the sea level, in lower montane rain forest in the sense of Breedlove (1981) or "bosque tropical perennifolio" in the sense of Rzedowski (1978). Some common species in this forest are Quercus lancifolia Schltdl. & Cham., Q. corrugata Hook., Calatola costaricensis Standl., Louteridium parayi Miranda, Justicia borrerae (Hemsl.) T.F.Daniel, Spathacanthus hahnianus Baill, and Bauhiniapansamalana Donn.Sm.

Interrelationships: -Stenanona migueliana most closely resembles S. stenopetala that also occurs in Chiapas. Differences between the two species are summarized as following: S. stenopetala has pedicels 9-23 mm long, sepals 2-3 mm long, ovules uniseriate, and the surface of monocarps smooth, minutely verrucose; whereas S. migueliana has pedicels 20-40 mm long, sepals 3-6 mm long, ovules biseriate, and the surface of monocarps strongly tuberculate. Monocarps of S. migueliana resemble those of S. tuberculata from Honduras in the tuberculate surface and distinct costa; however, S. tuberculata has flowers borne on very short pedicels, 2-5 mm long with longer sepals 6-15 mm long, whereas S. migueliana has longer pedicels and shorter sepals. Phenology: -Flowers have been collected and observed in the months of February (immature flower), July and August. The fruits have been observed and collected in July, August and September. Both structures have never been observed on the same plant.

We wish to thank Christopher Davidson and Sharon Christoph for financing visits to the type locality; Andrew Vovides, Lars Chatrou and Lubbert Westra for reviewing the manuscript and providing many useful comments. We are particularly grateful to Héctor Gómez Domínguez, Ana Celia Montes de Oca and friends of the Herbarium Eizi Matuda. Finally we thank Manuel Escamilla that provided the excellent illustration of S. migueliana.